Infrared cutoff film

ABSTRACT

An infrared cut-off layer containing an ITO powder is formed on one surface of a base film, to form an infrared cut-off film. The ITO powder has a minimum value of a diffused-reflection-functional logarithm, logf(R d ), at a light wavelength of 470 nm or lower, which logarithm is measured on the basis of the following equation, f(R d )=(1−R d ) 2 /2R d =α/S (R d : a relative reflectance to a standard sample, α: an absorption coefficient, S: a scattering coefficient, formulated for a diffused reflection light, and the minimum value of −0.1 or less. There is provided an infrared cut-off film having a hue of blue and sufficient transparency.

TECHNICAL FIELD

The present invention relates to an infrared cut-off film which isaffixed on, for example, a windowpane of a building or a car mainly inorder to cut-off the infrared of sun light.

TECHNICAL BACKGROUND

Conventionally, there is used an functional film having a infraredcut-off function, which film shows optical transmission properties to alight in a visible light region and which film reflects or absorbs alight in a infrared region, mainly for inhibiting the thermal influenceof radiated sun light. For example, the functional film adherent to awindowpane of a building or a car reduces heat, even when a solarradiation is directly received through the windowpane. Further, insummer, the increase of room temperature is reduced so that coolingefficiency is increased. Furthermore, it gives an additional effect,e.g., the prevention of shattering of the windowpane in a case of awindowpane break.

The above infrared cut-off film has a multi-layered structure, forexample, in which a protective layer is stacked on the front surface ofa base film and an infrared cut-off layer and an adhesive layer arestacked on the reverse surface in this order. And, the infrared cut-offfilm is used by affixing the adhesive layer onto a glass or the like.Conventionally, the infrared cut-off layer is formed on a base film byusing an infrared absorbent of imonium, aminium or ananthraquinone-containing compound or an infrared reflecting agent ofZnO, SnO₂ or a phthalocyanine-containing pigment as an infrared cut-offagent and forming a layer of the infrared cut-off agent by a vacuumdeposition method, a spattering method or a method in which a coatingcomposition obtained by dispersing the infrared cut-off agent in aproper resin and used for a infrared cut-off layer is applied.

However, the conventional infrared cut-off agent is colored to have, forexample, a puce or cobalt color. As a result, it has poor transparencyof a visible light transmittance of 50% or lower. Otherwise, it cuts offonly infrared radiation in a long wavelength region of 1000 nm or more,or 1500 nm or more or it cuts off only infrared radiation in a verynarrow range of wavelength region.

Thus, a powder of indium tin oxide (ITO, hereinafter) receives attentionas a material for improving the defects of the conventional infraredcut-off agent, and it is actually used.

Conventional infrared cut-off films comprising an ITO powder in aninfrared cut-off layer have a hue of blue-green or green in most casesand the conventional infrared cut-off films do not have sufficienttransparency. Further, a blue film having a sense of transparency isgenerally preferred as an infrared cut-off film used by affixing it on awindowpane or the like. Therefore, the conventional infrared cut-offfilms have not sufficiently satisfied the above requirement.

Therefore, it is an object of the present invention to provide aninfrared cut-off film having a hue of blue and sufficient transparencyin spite of the use of an ITO powder.

DISCLOSURE OF THE INVENTION

The present invention provides an infrared cut-off film having aninfrared cut-off layer in which a powder of indium tin oxide isdispersed,

wherein the powder of indium tin oxide has a minimum value of adiffused-reflection-functional logarithm, logf(R_(d)), at a lightwavelength of 470 nm or lower, which logarithm is measured on the basisof the following equation formulated for a diffused reflection light,

f(R _(d))=(1−R _(d))²/2R _(d) =α/S

 in which R_(d) is a relative reflectance to a standard sample, α is anabsorption coefficient and S is a scattering coefficient,

 and the above minimum value is −0.1 or less.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows a section view of an example of the layer structure of aninfrared cut-off film in the embodiment of the present invention.

FIG. 2 shows a section view of another example of the layer structure ofan infrared cut-off film in the embodiment of the present invention.

FIG. 3 shows a diagram of diffused-reflection-functional logarithms,logf(R_(d)), of the ITO powders used in Examples and ComparativeExamples in the present invention.

MOST PREFERRED EMBODIMENT FOR PRACTICING THE INVENTION

The present inventors have remarked the absorption spectrum of amaterial in a powder state in an optical measurement as an index whichdetermine the hue and transparency of ITO powder. In pages 331 to 332 ofthe literature “4th edition, Experimental Chemical Lecture 7, SpectrumII” (published by Maruzen K. K.), the following description is present.When the surface of a sample obtained by compression molding a materialin a powder state is irradiated with light, a reflective light from apowder layer may be thought to be the transmitted light of a crystal.The following “equation of Kubelka and Munk” is formulated with regardto this diffused reflection light,

f(R _(d))=(1−R _(d))²/2R _(d) =α/S  (1)

wherein R_(d) is a relative reflectance to a standard sample, α is anabsorption coefficient and S is a scattering coefficient.

This relative reflectance, R_(d), is measured and logf(R_(d)) iscalculated on the basis of the equation, whereby an absorption spectrumis obtained.

The present inventors measured of various ITO powders for a relativereflectance to a standard sample, and converted the measured values bythe above equation (1) to obtain spectrums of logf(R_(d))) which is alogarithm to a diffused reflection function. Further, these ITO powderswere used to prepare infrared cut-off film samples. As a result, it hasbeen found that infrared cut-off films obtained by using an ITO powderwhich has the minimum value of a diffused-reflection-functionallogarithm, logf(R_(d)), shown as a spectrum, at a light wavelength of470 or less and has the above minimum value of −0.1 or less, have a bluehue having a sufficient sense of transparency. Therefore, the infraredcut-off film of the present invention has been obtained on the basis ofthe above finding. The infrared cut-off film of the present invention ischaracterized in that the ITO powder which has the minimum value of adiffused-reflection-functional logarithm, logf(R_(d))), measured on thebasis of the above equation (1), at a light wavelength of 470 or lessand has the above minimum value of −0.1 or less is used in an infraredcut-off layer.

Further, with regard to the component molar ratio of the ITO powder inthe present invention, oxygen is preferably 0.5 to 10 per 100 of indium.

The embodiment of the present invention will be explained hereinafter.

In the infrared cut-off film of the present invention, an infraredcut-off layer is laminated on at least one surface of a base film and anadhesive layer is laminated on the above surface. As a preferred stateof a practical layer structure, for example, there is cited a state inwhich the infrared cut-off layer 2 and a protective layer 3 arelaminated in this order on the front surface of the base film 1, and onthe other hand, the adhesive layer 4 and a separating material 5 arelaminated in this order on the reverse surface of the base film 1, asshown in FIG. 1. Otherwise, as shown in FIG. 2, there is also cited astate in which the protective layer 3 is laminated on the front surfaceof the base film 1 and the infrared cut-off layer 2, the adhesive layer4 and the separating material 5 are laminated on the reverse surface ofthe base film 1 in this order. In any case, the separating material 5 ispeeled off from the adhesive layer 4 and the adhesive layer 4 adheres toa glass, etc., for use.

The infrared cut-off layer in the infrared cut-off film of the presentinvention is formed by, in one case, mixing and dispersing an ITO powderwhich has the above properties, that is, which has the minimum value ofa diffused-reflection-functional logarithm, logf(R_(d))), at a lightwavelength of 470 or less and has the above minimum value of −0.1 orless, in a resin having transparency, to form a coating composition forthe infrared cut-off layer, and applying the coating composition ontothe base film. In another case, the infrared cut-off layer is formed asa metal thin film layer by a vacuum deposition method or a spatteringmethod. The method of applying the coating composition for the infraredcut-off layer onto the base film includes a mayer bar coating method, adoctor blade coating method, a gravure coating method and a dip coatingmethod. The thickness of the applied coating is preferably 0.5 to 10 μm,more preferably 0.5 to 5 μm. Further, the thickness of the metal thinfilm layer formed by the vacuum deposition or spattering method ispreferably 5 to 500 Å, more preferably 50 to 300 Å. When the thicknessis thinner than each lower limit of the above ranges, infrared cut-offproperties are decreased. When the thickness excesses each upper limitof the above ranges, a surface is formed in a mirror state so that avisible light transmittance is liable to be too low.

Materials constituting each layer of the infrared cut-off film of thepresent invention will be described in detail, hereinafter.

A. Base Film

Known transparent films may be used as a base film. Specific examplesthereof include various resin films such as polyethylene terephthalate,polyethylene naphthalate, triacetyl cellulose, polyallylate, polyether,polycarbonate, polysulfone, polyether sulfone, cellophane, polyethylene,polypropylene and polyvinyl alcohol. These resin films may be preferablyused.

B. ITO Powder as an Infrared Cut-off Agent

As an ITO powder used as an infrared cut-off agent in the infraredcut-off layer in the present invention, there is used an ITO powderwhich has the minimum value in the spectrum of adiffused-reflection-functional logarithm, logf(R_(d)), at a lightwavelength of 470 or less and has the above minimum value of −0.1 orless, as described above. From the viewpoint of transparency anddispersibility, the ITO powder preferably has an average particlediameter of 100 nm or less, more preferably 50 nm or less, the mostpreferably 25 to 35 nm.

In the present invention, the spectrum of the abovediffused-reflection-functional logarithm is obtained by measuring atotal reflection spectrum in a wavelength range of 200 to 2,600 nm by a60 mm φ integrating sphere photometry method (aluminum oxide is used asa standard material), and converting the measured total reflectionspectrum by “the equation of Kubelka and Munk” (the above equation (1)).The measurement is carried out with a spectrophotometer, e.g., U-4,000,supplied by Hitachi, Ltd.

For example, there is used an ITO powder which is obtained by reactingan aqueous solution containing water-soluble salts of In and a smallamount of Sn with alkali to co-precipitate hydroxides of In and Sn andobtain the co-precipitated materials as raw materials, and thencalcining these raw materials under heating in a reducing atmospheresuch as CO, NH₃ or H₂, to convert an oxide. The proper adjustments ofthe component composition of indium, tin and oxygen and calcinationconditions gives an ITO powder which has the above-mentioned minimumvalue of the logarithm to a diffused reflection function. As for thecomponent molar ratio thereof, In/Sn/O₂ is preferably 100/5 to 10/0.5 to10, more preferably 100/5 to 10/0.5 to 2. The above ITO powder has theshortest infrared cut-off wavelength of 800 nm and is remarkablyexcellent in infrared cut-off function. Further, the color of theinfrared cut-off film of the present invention in which an ITO powderlike above is dispersed is a blue color having a sense of transparencyowing to the reflection of the color of the ITO powder. Users generallylike a film having a blue color. When this requirement is present, theabove ITO powder can provide a film which sufficiently satisfy the aboverequirement.

C. Resin Used When an Applied Layer is Formed as an Infrared Cut-offLayer

No special limitation is imposed on a resin with/in which the powder ofthe infrared cut-off agent is mixed and dissolved, so long as it hasfilm properties and transparency and has adhesive properties to the basefilm. In particular, an ultraviolet curing resin obtained byincorporating a photo-radical polymerization initiator and/or aphoto-cation polymerization initiator into a monomer containing at leastone kind of acrylic compound or epoxy compound, is preferably used. Theincorporation of the acrylic compound is preferred for controlling theviscosity and crosslinking density of the ultraviolet curing resin, andproperties of a coating composition and an applied film, such as heatresistance and chemical resistance.

The epoxy compound includes glycidyl ethers such as tetramethyleneglycol diglycidyl ether, propylene glycol diglycidyl ether, neopentylglycol diglycidyl ether and bisphenol A-diglycidyl ether, epoxy esterssuch as 2-hydroxy-3-phenoxypropylacrylate and bisphenolA-diepoxy-acrylic acid adduct, and monomers and oligomers formed of thefollowing chemical formulae, such as an alicyclic epoxy,

The acrylic compound includes monofunctional acrylates such as laurylacrylate, ethoxydiethylene glycol acrylate, methoxytriethylene glycolacrylate, phenoxyethyl acrylate, tetrahydrofurfuryl acrylate, isobornylacrylate, 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate and2-hydroxy-3-phenoxy acrylate, polyfunctional acrylates such as neopentylglycol diacrylate, 1,6-hexanediol diacrylate, trimethylolpropanetriacrylate, pentaerythritol triacrylate, pentaerythritol diacrylate anddipentaerythritol hexaacrylate, acrylic acid derivatives such astrimethylolpropane acrylic acid benzoate and trimethylpropane acrylicacid benzoate, monofunctional methacrylates such as 2-ethylhexylmethacrylate, n-stearyl methacrylate, cyclohexyl methacrylate,tetrahydrofurfuryl methacrylate, 2-hydroxyethyl methacrylate and2-hydroxybutyl methacrylate, methacrylic acid derivatives ofpolyfunctional methacrylates such as 1,6-hexanediol dimethacrylate,trimethylolpropane trimethacrylate and glycerol dimethacrylate andmonomers and oligomers of urethane acrylates such as glyceroldimethacrylate hexamethylene diisocyanate and pentaerythritoltriacrylate hexamethylene diisocyanate. Further, a compound containingat least one compound of the following chemical formula is used,

the others are alkyl group, and a lower alkyl group having about 1 to 6carbon atoms is preferred as the above alkyl group.

The photo-radical polymerization initiator includes, for example,acetophenone compounds of the following chemical formulae,

and, for example, benzoin compounds of the following chemical formulae.

The photo-cation polymerization initiator includes compounds of thefollowing chemical formulae. These compounds may be used alone or incombination.

The amount of the photo-radical polymerization initiator and/or thephoto-cation polymerization initiator is preferably in the range of 0.1to 10% by weight based on the main agent. The basis of the amount is asfollows. When the amount is smaller than 0.1% by weight or it is greaterthan 10% by weight, curing by ultraviolet is insufficient.

Further, the transparency of the resin constituting the infrared cut-offlayer is preferably as high as possible. It is preferable that lighttransmittance of at least 80%, preferably at least 90%, measured by “JISK7105” is secured. In order for the infrared cut-off layer to be easilyapplied onto the base film and to have high adhesive properties, wettingcharacteristics are preferably as high as possible. Concretely, thewetting index of the surface (surface tension: dyn/cm) according to “JISK6768” is preferably 50 or less, more preferably 36 to 46.

With regard to the amount ratio of the ITO powder and the resin whichconstitute the coating composition for an infrared cut-off layer, ITOpowder/resin is 90/10 to 60/40 in a weight ratio, preferably 85/15 to65/35, more preferably 80/20 to 70/30. In the above amount ratio range,even a thin layer of about 1 μm shows fine infrared cut-off propertiesso that a film having high transparency and little haze can be obtained.When the amount ratio of the ITO powder is larger than 90% by weight, afilm is liable to be colored too much with the ITO powder or the degreeof a haze is liable to be too high. And, a metallic sheen is alsoincreased, the peeling of the infrared cut-off layer or a cohesivefailure is caused and, further, the adhesive properties to the base filmare poor. Further, when the amount ratio of the ITO powder is smallerthan 60% by weight, an intended infrared cut-off function is notattained in some cases.

D. Pigment

In the present invention, a pigment such as ZnO, SnO₂, TiO₂, etc., maybe incorporated in the infrared cut-off layer. That is, the pigmenttogether with ITO powder is mixed with the resin to form an infraredcut-off layer. The pigment performs an infrared cut-off functiontogether with the ITO powder. The infrared cut-off wavelength rangethereof is 1,200 to 2,500 nm. Therefore, the combination of the pigmentand the ITO powder can set the amount ratio of the ITO powder in theresin at a low degree in the above range without decreasing cut-offproperties of 800 to 2,500 nm infrared wavelengths which are so-called anear infrared range. Owing to this, it becomes possible to decrease theamount of ITO powder which is expensive so that cost-reduction isattained. These pigments are required to have an average particlediameter of 100 nm or less for inhibiting the metallic sheen orattaining a fine electromagnetic wave transmittance.

E. Protective Layer

As a protecting agent which constitutes the protective layer, generally,there may be used a resin which is curd by an electrolytic dissociationradiation, heat or combination of these.

The radiation curable resin is selected from compositions obtained byproperly mixing monomers, oligomers or prepolymers containingpolymerizable unsaturated bond, such as an acryloyl group, amethacryloyl group, an acryloyloxy group and a methacryloyloxy group.Examples of the monomers include styrene, methyl acrylate, methylmethacrylate, methoxy polyethylene methacrylate, cyclohexylmethacrylate, phenoxyethyl methacrylate, ethylene glycol dimethacrylate,dipentaerythritol hexaacrylate, trimethylolpropane trimethacrylate, etc.The oligomers and the prepolymers include acrylates such as polyesteracrylate, polyurethane acrylate, epoxy acrylate, polyether acrylate,alkyd acrylate, melamine acrylate and silicone acrylate, unsaturatedpolyester and epoxy compounds. These may be used alone or incombination. The amount of the monomer is adjusted at a low degree whenthe flexibility of a cured film is required. For decreasing acrosslinking density, further, the use of an acrylate-containing monomerhaving one function or 2 functions is preferred. Reversely, when severeendurances such as heat resistance, abrasiveness and solvent resistanceare required for the cured film, the amount of the monomer is increasedand it is preferred to use an acrylate-containing monomer having a least3 functions.

It is sufficient to irradiate a radiation such as an ultraviolet ray, anelectron ray or X-ray for curing the aboveelectrolytic-dissociation-radiation-curable resin. A polymerizationinitiator may be properly added as required. When an ultraviolet raycures the resin, a photopolymerization initiator must be added. Thephotopolymerization initiator includes acetophenones such as diethoxyacetophenone, 2-hydroxy-2-methyl-1-phenylpropane-1-one, benzildimethylketal, 1-hydroxycyclohexyl-phenylketone and 2-methyl-2-morpholino(4-thiomethylphenyl)propane-1-one, benzoin ethers such as benzoin methylether, benzoin ethyl ether, benzoin isopropyl ether and benzoin isobutylether, benzophenones such as benzophenone, o-benzoyl methyl benzoate,4-phenylbenzophenone, 4-benzoyl-4′-methyl-diphenyl sulfide,4-benzoyl-N,N-dimethyl-N-[2-(1-oxo-2-propenyloxy)ethyl]benzenemethanaminium bromide and (4-benzoylbenzyl) trimethyl ammonium chloride,thioxanthones such as 2,4-diethylthioxanthone and1-chloro-4-dichlorothioxanthone, and 2,4,6-trimethylbenzoyl diphenylbenzoyl oxide. These may be used alone or in combination. Further, anamino compound such as N,N-dimethylparatoluidine or4,4′-diethylaminobenzenephenone is incorporated as a promoter(sensitizer) for use.

Further, as a resin used for the protecting agent, in particular, it ispreferred to use an ultraviolet-curable epoxy compound in view of itsexcellent hardness and transparent adhesive properties. Specific epoxycompound includes glycidyl ethers such as tetramethylene glycoldiglycidyl ether, propylene glycol diglycidyl ether, neopentyl glycoldiglycidyl ether and bisphenol A-diglycidyl ether, and epoxy esters suchas 2-hydroxy-3--phenoxypropyl acrylate and bisphenol A-diepoxy-acrylicacid adduct. Further, as the polymerization initiator, a photo-radicalpolymerization initiator and/or a photo-cation polymerization initiatormay be used. The same initiators as those used in the above infraredcut-off layer are cited. The amount thereof is preferably in the rangeof 0.1 to 10% by weight based on the main agent. When the above amountis smaller than 0.1% by weight or lager than 10% by weight, anultraviolet curing is liable to be insufficient.

F. Adhesive Layer

As an adhesive agent forming the adhesive layer, an acrylic adhesiveagent composed of a resin containing, for example, acrylic acid ester ormethacrylic acid ester as a main component is used. A metalchelate-containing, isocyanate-containing or epoxy-containing linkingagent as a hardener is mixed with the above agent for use as required.These linking agents are used alone or in combination. The aboveadhesive agent is practically preferably incorporated such that adhesionstrength (according to JIS Z0237) as an adhesive layer is adjusted inthe range of 100 to 2,000 g/25 mm. Further, generally, the thickness ofthe adhesive layer after drying is preferably 10 to 50 μm. Further, theproper incorporation of an ultraviolet absorbent into the adhesive layergives an ultraviolet cut-off effect together. As the ultravioletabsorbent, p-t-butylphenyl salicylate, 2-hydroxy-4-methoxybenzophenone,2-hydroxy-4-octoxybenzophenone, 2,2′-dihydroxy-4-methoxybenzophenone,2′-(2′-hydroxy-5-methylphenyl)benzotriazol,2-(2′-hydroxy-3′-t-butyl-5′-methylphenyl)-5-chlorobenzotriazol, or2-(2′-hydroxy-3′,5′-di-t-butylphenyl)benzotriazol is preferably used.

G. Other materials

Solvents added to each coating composition of an infrared cut-off layer,a protective layer and an adhesive layer

Each coating composition for the protective layer, the adhesive layerand the infrared cut-off layer may properly contain organic solventssuch as benzene, toluene, acetone, methyl ethyl ketone, isophorone andcyclohexanone as a solvent. These organic solvents may be added alone orin combination.

Surfactants added to the coating composition for an infrared cut-offlayer

A very small amount of surfactant (e.g., nonionic surfactant) may beadded to the coating composition for the infrared cut-off layer forimproving the dispersibility of an ITO powder.

Further, while the film of the present invention has the principalpurpose of an infrared cut-off, an ultraviolet cut-off effect is alsoobtained by properly adding the ultraviolet absorbent, as describedabove, into at least one layer other than the above adhesive layersimilarly to the case of the above adhesive layer.

EXAMPLES

The effects of the present invention will be described with reference toExamples, hereinafter.

Samples A to E of five kinds of ITO powders each of which has differentcalcination conditions and component molar ratio from those of theothers, were optically measured for relative reflectances to a standardsample with a spectrophotometer (U-4,000, supplied by Hitachi, Ltd.).Spectrums of diffused-reflection-functional logarithms were measured onthe basis of the above equation (1) in the light wavelength range of 200to 2,600 nm, and the minimum values thereof were examined. In FIG. 3,the results thereof are graphed. Among these samples A to E, only thesample A satisfied the conditions of the present invention. The otherfour samples B to E deviated from the conditions of the presentinvention. Table 1 shows the minimum values of the absorption spectrumsof these ITO powders A to E and wavelengths at those values.

TABLE 1 A B C D E Minimum value −0.35 −0.35 −0.32 −0.04 −0.01 Wavelength(nm) 425 485 480 425 420

Preparation of Infrared Cut-off Films Example 1

ITO powder of sample A (In/Sn/O₂=100/7.5/0.9)38 parts

An ultraviolet curable resin (trade name: Z-7501, supplied by JSR) 31parts

Solvent (methyl isobutyl ketone) 31 parts

These components were used to prepare a coating composition for aninfrared cut-off layer. The coating composition was applied onto thesurface of a 50 μm thick polyethylene terephthalate film (trade name:Emblet MS, supplied by UNITIKA Ltd.) by a mayer bar coating method suchthat the coating film after drying had a thickness of 1.5 μm. Thecoating film was dried at 105° C. for 1 minute, to form an infraredcut-off layer, whereby the infrared cut-off film of Example 1 wasobtained. The infrared cut-off film was measured for an opticaltransmission spectrum with the above-mentioned spectrophotometer, toshow that it had excellent infrared cut-off properties.

Comparative Example 1

An infrared cut-off film of Comparative Example 1 was obtained in thesame manner as in Example 1 except that Sample B was used as an ITOpowder.

Comparative Example 2

An infrared cut-off film of Comparative Example 2 was obtained in thesame manner as in Example 1 except that Sample C was used as an ITOpowder.

Comparative Example 3

An infrared cut-off film of Comparative Example 3 was obtained in thesame manner as in Example 1 except that Sample D was used as an ITOpowder.

Comparative Example 4

An infrared cut-off film of Comparative Example 4 was obtained in thesame manner as in Example 1 except that Sample E was used as an ITOpowder.

Tests of a Hue and Transparency

The infrared cut-off films of Example 1 and Comparative Examples 1 to 4were evaluated for a hue, a HAZE value and a light transmittance(550nm). Table 2 shows the results. Further, the hue, the HAZE value and thelight transmittance (%) shown in Table 2 were measured as follows.

Hue: According to a visual observation.

HAZE value: According to a measuring method of a haze value, defined inJIS K7105.

Light transmittance: Whole light transmittance defined in JIS K7105 wasmeasured, and the value of the whole light transmittance at a wavelengthof 550 nm was used.

TABLE 2 Example 1 CEx. 1 CEx. 2 CEx. 3 CEx. 4 Hue Blue Green Green BlueBlue HAZE value  1.2  3.6  3.7  2.1  2.0 Light 86.0 81.9 82.2 80.8 80.9transmittance (%) CEx. = Comparative Example.

As is apparent from Table 2, the infrared cut-off film of the presentinvention had a blue hue, had a small Haze value and was free of a haze.And, the infrared cut-off film of the present invention had a high lighttransmittance and excellent transparency. On the other hand, Each filmof Comparative Examples was inferior to the infrared cut-off film of thepresent invention in transparency. Further, the films of ComparativeExamples 1 and 2 had a conventional type green color so that they werepoor in visual appreciation.

INDUSTRIAL UTILITIES

As described above, according to the present invention, there isprovided an infrared cut-off film which surely has excellent infraredcut-off properties, has a blue hue excellent in visual appreciation andhas sufficient transparency by using an ITO powder in which the minimumvalue of a diffused-reflection-functional logarithm is −0.1 or less at alight wavelength of 470 or less, into an infrared cut-off layer.

We claim:
 1. An infrared cut-off film having an infrared cut-off layer which is formed on a film by using a coating composition obtained by mixing and dispersing a powder of indium tin oxide in a resin having transparency, wherein the powder of indium tin oxide has a minimum value of a diffused-reflection-functional logarithm, logf(R_(d))), at a light wavelength of 470 nm or lower, which logarithm is measured on the basis of the following equation formulated for a diffused reflection light, f(R _(d))=(1R _(d))²/2R _(d) =α/S  in which R_(d) is a relative reflectance to a standard sample, α is a an absorption coefficient and S is a scattering coefficient, and the above minimum value is −0.1 or less, and the resin having transparency is an ultraviolet curable resin obtained by incorporating a photo-cation polymerization initiator into a monomer containing at least one acrylic compound or epoxy compound.
 2. The infrared cut-off film according to claim 1, wherein the powder of indium tin oxide has a molar ratio of 0.5 to 10 of oxygen per 100 of indium.
 3. The infrared cut-off film according to claim 1, wherein the powder of indium tin oxide has a molar ratio of 5 to 10 of tin and 0.5 to 10 of oxygen per 100 of indium.
 4. The infrared cut-off film according to claim 1, wherein the applied layer has a thickness of 0.5 to 10 μm.
 5. The infrared cut-off film according to claim 1, where in the coating composition has an indium tin oxide/resin weight ratio in the range of 90/10 to 60/40.
 6. The infrared cut-off film according to claim 1, wherein the coating composition in which the powder of indium tin oxide is mixed and dissolved further contains a pigment having an average particle diameter of 100 nm or less.
 7. The infrared cut-off film according to claim 1, wherein the powder of indium tin oxide has an average particle diameter of 100 nm or less. 